Fun-loving scoring prodigy, anti-Soviet Czech nationalist, champion, moping quitter, maturing superstar, enthusiastic Russophile. Now, four games into his return to the N.H.L. with the Philadelphia Flyers after three years in the Kontinental Hockey League, Jagr is reinvented again, as wise elder statesman and exemplar of hard work.

He is not the only one to change since he last played in North America, in 2008. The league he came back to also has a new look.

“How to explain it?” he mused in his still heavily Czech-accented English. “It’s different for one reason. The puck is everywhere. Not as much on your stick. The players don’t play the position game as much as we used to play. A lot of young guys go up and down, shoot the puck, go for the rebounds.

“You’re getting tired quicker because the body has to react where the puck is going to go,” he said of the faster, more frenetic N.H.L. of 2011. “You cannot read it, because you don’t have the puck on your stick.”

Jagr made it sound impossible for a 39-year-old like himself to keep up, but in fact he is keeping up quite well in this newest chapter in his astonishing career. On Saturday night, he set up Danny Briere for the Flyers’ first goal in a 3-2 overtime loss to the Los Angeles Kings, their first defeat in four games this season.

When Giroux was asked if Jagr would be able to keep up with him and van Riemsdyk over the course of the season, Giroux said, “He looks fast out there — we’re trying to keep up with him.”

Fans who remember the Jagr of the 1990s and early 2000s, the one who was often accused of dogging it through various contract disputes and losing streaks, will be shocked to learn about the diligence of the Jagr of today.

During training camp last month at the Flyers’ practice rink in Voorhees, N.J., Jagr got his own key so he could let himself in at night for an extra round of solitary skating.

“Motivation for everybody else to follow,” Giroux said.

At Voorhees the day before Saturday’s game, one Flyer after another clomped through the dressing room, coming and going after a vigorous hourlong practice. But no Jagr.

It turned out he was one of just three players left on the ice, maneuvering with a stick rigged with a 20-pound weight on its blade. Later, he stood in the corner of the rink, talking body positioning and demonstrating various stances with Jody Shelley, a Flyers enforcer serving a 10-game suspension for boarding.

In the dressing room, Shelley was uncharacteristically circumspect when asked what Jagr was showing him. “Oh, nothing,” the usually voluble Shelley said. “Just Jaromir sharing some of his knowledge.”

“You owe me 50 for that,” Jagr said, flashing a grin at Shelley.

Jagr’s first arrival in North America came in Pittsburgh in 1990. A star in his Czech hometown, Kladno, he was a big, mulleted 18-year-old who wore No. 68 for the Prague Spring and who, as a schoolboy, carried a picture of the anti-Soviet crusader Ronald Reagan.

He looked and played like Mario Lemieux — “Jaromir,” it was pointed out, is an anagram for “Mario Jr.” — and together they led the Penguins to Stanley Cups in his first two N.H.L. seasons. He remained with the Penguins until 2001, winning five league scoring championships and a most valuable player award, but no more Cups. By the end of his tenure, he had asked to be traded a couple of times; he had soured on Pittsburgh, and once-adoring Penguins fans had soured on him.

Jagr was dealt to Washington, where he signed a seven-year contract worth about $77 million. But after two and a half miserable, underachieving seasons as the increasingly reluctant go-to guy, he was dealt to the Rangers in January 2004.

There he thrived under Coach Tom Renney; he still calls Renney “a really smart guy” and a “good human being” whom he respects for being able to admit mistakes, “something I never heard from a coach.” Jagr set single-season Rangers records for goals (54) and points (123).

With Jagr leading the way and charming fans and reporters with consistent good nature, the Rangers reached the second round in 2007 and 2008, the furthest the team has gotten at any point since 1997.

Jagr was suited for Russia. In 2001, he had converted to Orthodox Christianity. Around the same time, he got into expensive tax disputes with the I.R.S. and had to pay off Internet gambling debts.

Jagr loved Russia. “You got such freedom, it’s hard to believe,” he said in a 2008 interview with Play Magazine. “In the U.S., you have so many rules, everything’s regulated and structured. When you make a mistake, you pay for it — a lot.”

He added, “In Russia, you don’t have to worry if you make a mistake.”

On the ice, there was disappointment. Avangard struggled in Jagr’s first two years but won the K.H.L. regular-season championship last season — only to fall in the second round of the playoffs.

But there was far worse. In 2008, Jagr’s 18-year-old linemate, Alexei Cherepanov, suddenly collapsed while talking to Jagr on the bench during a game and died soon after of cardiac arrest. Jagr, badly shaken for days, called it “a shock, which can’t be described.”

But Jagr will brook no belittling of the K.H.L. in comparison with the N.H.L.

“Be careful what you’re saying because it’s a totally different game,” he said. “There’s a lot of great players there who can play on the big ice, but maybe they would have a problem here. But the other way around, it’s the same thing — a lot of guys dominating here would have a problem on the big ice.”

He said that the frenetic pace of the current N.H.L. was not possible in Russia.

“In the K.H.L., you’re even more patient at your position because the rink is so big, you cannot play that way,” he said. “You would be dead after two shifts, to chase the puck all over the ice, and you still wouldn’t have it.”

Now Jagr is going through another reinvention: he is a Philadelphia Flyer, after years of being a hated Penguin, Capital and Ranger. That is because he publicly spurned contract offers from Pittsburgh and Detroit, peeving both organizations, and accepted the Flyers’ richer $3.3 million deal for one year.

“It wasn’t the most money — trust me,” Jagr said, laughing once more. He said there were offers from still other teams, though not the Rangers. But it was the Flyers, who had blown up their underachieving team by trading away the star forwards Mike Richards and Jeff Carter, who gave him the best chance to play. “And,” he said, “I felt they were interested.”

Jagr said he would see how this season went, then decide if he wants to take another spin around the N.H.L. before closing out his career with his hometown club in Kladno.

Did he have any idea yet if one final season in the N.H.L. would be enough?